MRI-compatible anesthesia gas masks for animals and MRI-compatible platforms for animal surgery are commercially available items; see for example products of Stoelting Co (US), 2Biological Instruments (IT) etc. As designed by their producers, these gas anesthesia platforms and mouse, rat, dog etc. masks provide easy positioning of an animal during anesthesia and surgery and often allow for anesthetization and positioning of the animal outside of a stereotaxic device and for dorsal surgery. The animal's teeth are usually placed over an incisor bar and the mask slid forward until the cone fits snugly around the animal's nose, so that no nose clamp is required. The platform is then lifted onto an appropriate stereotaxic device, providing positioning of the animal. The head of the animal is not perfectly conical, however. Eyes, ears and other organs of the animal do not perfectly fit the conical mask, and hazardous leakage of anesthetization gas often occurs within the close environment of the laboratory. Cases in which laboratory personnel collapsed after breathing anesthetization gas applied to experimental animals have been reported in the literature.
US patent application 2004/0216737 discloses an anesthesia system for administering an anesthetic gas to the nose of an animal. The anesthesia system comprises a mask having a receptacle adapted to surround and form a fluid path to the animal's nose; a breather enclosure forming an air exchange chamber, the breather enclosure comprising a connector configured for coupling with the mask to connect the receptacle and air exchange chamber in fluid communication; an inlet hub extending inside the air exchange chamber and forming an inlet port through a wall in the breather enclosure, the inlet port being adapted to convey the anesthetic gas into the chamber and to the mask; and a check valve connected with the inlet hub and extending within the air exchange chamber, the check valve being operable in response to relative pressure in the air exchange chamber between an open position, which permits anesthetic gas to enter the air exchange chamber, and a closed position, which substantially prevents anesthetic gas from entering the air exchange chamber, wherein the check valve moves to the open position in response to vacuum pressure created when the animal inhales, the check valve being normally biased in the closed position.
U.S. Pat. No. 6,363,931 discloses an occluder for supporting and preventing escape of anesthesia gases through face masks when not in use, comprising: a C-shaped support base with a flat base plate adapted to fit beneath a surgical mattress, a side plate located in a plane normal to that of the base plate having a bottom edge contiguous with the base plate and having a height equal to the thickness of a standard surgical mattress, and a top plate contiguous with an upper edge of the side plate, the top plate being in a plane parallel to that of the base plate; and a solid cylindrical support shaft supported on and extending upwardly from the top plate, the cylindrical support shaft having a main body portion approximately 15 mm in diameter.
U.S. Pat. No. 4,633,890 discloses an apparatus for preventing the undesirable egress of anesthetic gas into ambient atmosphere, comprising a tube having one end connected to an anesthesia machine and its second end being a free end; the anesthesia machine supplying anesthetic gas to the tube; the free end being removably connectable to a breathing passage of a patient; an obturator post connected to the anesthesia machine and constructed to sealingly engage the free end, for preventing the undesirable egress of the anesthetic gas into the atmosphere of an operating theater when the free end is disconnected from the breathing passage; and a bore passing through the obturator post and communicating with exhaust means.
None of the above provides a simple solution for anesthetization and precise positioning of the animal within an MRI device. Hence an MRI-compatible and safe mask would fulfill a long felt need.